The invention relates to a prosthetic component with a pneumatic device for articulation of the knee.
Such a prosthetic component is an essential element of an artificial leg prosthesis called an "above the knee", that is to say which has a foot, an ankle, a lower part of the leg hereinafter called a "leg", a knee and a socket for receiving the stump of the thigh.
The patient can perform a balancing movement with this type of prosthesis. If this movement is controlled in an appropriate manner, the ability to walk in a relatively natural way can thus be restored.
A large number of means for controlling the relative movement of the upper part of the prosthetic device (supporting the socket) with respect to its lower part (connected to the leg) are known from the prior art.
The basic function which this prosthetic device must perform is that of damping and propelling, which is generally provided by the use of springs, hydraulic or pneumatic cylinders, or by any combination of these means.
The British patent application GB-A-2,252,503, published on Aug. 12, 1992, gives an example of use of a pneumatic cylinder for controlling the movement of a prosthesis. The opening of the valve of the cylinder of the prosthetic component is controlled by a micro-processor as a function of the speed of walking. The use of a computer for producing the control signals for the valve of the cylinder as a function of the signal coming from an angle transducer between the thigh and the leg permits a sophisticated control of movements. However, this knee prosthesis component is pivoted about a fixed axis of rotation and therefore possesses movement characteristics rather far from those of a human knee.
The international patent application WO 93/22,991 published on Nov. 25, 1993 describes a mechanical articulation reproducing the kinematics of the normal human knee. The movement of the lower part of the articulation is guided by studs moving in curved grooves in the upper part, in such a manner that the axis of rotation is variable and no longer fixed.
The same kinematics can be produced by interconnection links as is shown in the European patent application EP-A1-0,590,386 filed by the German company Otto Bock Orthopadische Industrie and published on Apr. 6, 1994.
The international patent application WO 92/22,267 published on Dec. 23, 1992 has already shown a simultaneous embodiment of the above principles: a variable axis of rotation obtained by a set of links and a pneumatic cylinder having a function of damping and propulsion. The control of the flexure and extension of the articulation being however produced differently by the flow of a fluid in a hydraulic cylinder controlled by an electro-magnetic valve.
The pneumatic prosthetic component for articulation of he knee sold by the Proteval company under the name "Acphapend" has the advantages of the first three prior devices but is an entirely mechanical and pneumatic product, which is consequently simpler and more reliable.
In certain conditions of use, particularly for running, a prosthesis having a hydraulic system is more suitable. The device described in the WO 92/22,267 specification can thus represent a good compromise. However, the mass of fluid renders the device significantly heavier than an entirely pneumatic apparatus, and thus tiring for its user.
The European patent application EP-A1-0,628,296 filed by the Chas. A. Blatchford & Sons company and published on Dec. 14, 1994 describes a control system for a prosthesis which uses the same principles as those described in the GB-A-2,252,503 specification. The patient is also provided with a electronic circuit for automatic control. It is clear that the possibility of no longer having to make adjustments on the prosthetic component as such is a significant comforting factor for the patient; further, these adjustments can then be made during walking.
It is in taking account of all these constraints that the new prosthetic component for articulation of the knee according to the present invention has been conceived; an entirely mechanical and pneumatic product, similar to the product known under the "Acphapend" name, it also provides a little more closely the same characteristics, adjustable at will, as those of a hydraulic knee. Combining, on the one hand, the comfort of remote adjustment of the orthopaedic characteristics which are a feature of electronic systems and, on the other hand, the stiffness necessary in certain sporting activities exhibited only by hydraulic knees, whilst being lighter, more simple and more reliable than these latter, the invention offers advantages unknown at present in the state of the art.